Ceramic injector for fluid catalytic cracking unit

ABSTRACT

The invention relates to a feedstock injector ( 2 ′) for injecting an atomized hydrocarbon feedstock into a tubular-type reactor with substantially upward or downward flow that is intended to be used in a fluid catalytic cracking unit, having: at least one hollow cylindrical body ( 41 ); at least a first and a second inlet openings ( 40, 42 ) for respectively injecting a liquid hydrocarbon feedstock to be cracked and an atomizing gas into said cylindrical body ( 41 ); at least one contact chamber ( 46 ) arranged inside said hollow cylindrical body, in which said liquid hydrocarbon feedstock to be cracked and said atomizing gas are intended to be brought into contact in order to atomize said liquid hydrocarbon feedstock to be cracked; and at least one outlet opening ( 44 ) that opens on the inside of said reactor in order to eject said liquid hydrocarbon feedstock thus atomized. According to the invention, each element of the injector ( 2 ′) is formed of a ceramic material.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.15/326,613, filed Jan. 16, 2017, which claims the benefit ofPCT/EP2015/066897, filed Jul. 23, 2015, which claims priority from FR1457253 filed Jul. 28, 2014, which are herein incorporated in theirentireties for all purposes.

The present invention relates to a feedstock injector of a fluidcatalytic cracking (FCC) unit.

In an FCC unit, a hydrocarbon feedstock atomized into fine droplets isinjected then brought into contact, at high temperature, for examplefrom 520° C. to 550° C., with cracking catalyst grains circulating in areactor in the form of a dilute fluidized bed.

The reactors used are generally vertical reactors of tubular type, inwhich the catalyst moves following an essentially upward flow (riserreactor) or essentially downward flow (downer reactor). These reactorsare generally provided with at least one injector, with the aid of whichthe hydrocarbon feedstock is introduced into the reactor. Before beingintroduced into the reactor, the hydrocarbon feedstock is atomized intofine droplets inside the injector. Although there is no real consensusregarding the optimum diameter of the droplets, in general it is soughtto form droplets whose diameter is of the same order of magnitude as thediameter of the catalyst particles, namely less than 200 microns, forexample of the order of 70 to 80 microns.

This step of atomization of the feedstock by the injectors isparticularly important since it makes it possible to maximize the liquid(liquid hydrocarbon feedstock)-solid (catalyst) contact area, whichpromotes the heat transfer and contributes to the homogeneousdistribution of the hydrocarbons within the riser or downer reactor.

Generally, use is made of “two-phase” injectors, which have a hollowcylindrical body and two inlet openings through which the liquidhydrocarbon feedstock to be cracked and an atomizing gas, generallysteam, are respectively injected into said body. A contact chamber isarranged inside the body, in which the hydrocarbon feedstock and theatomizing gas are brought into contact in order to atomize thehydrocarbon feedstock. Once atomized, the hydrocarbon feedstock isejected via an outlet opening that opens into the reactor. Each injectoris inserted in a reactor wall so that one end of the injector comprisingthe outlet opening is located inside the reactor.

The injector is subject, on the one hand, to a corrosion induced by thesteam and by the hydrocarbon feedstock passing through the inside of thebody of the injector, and on the other hand to an external erosioninduced by the circulation of the catalyst inside the reactor.

In order to solve this problem, an injector made of special steels hasbeen proposed, the end of which located inside the reactor is optionallycoated with a layer of ceramic having a thickness of several hundreds ofmicrons. Although the injectors thus obtained display a betterresistance, this technique does not allow prolonged use of the injectorswithout maintenance or regular replacement owing to the substantialabrasion caused by the stream of catalyst passing in contact with theouter surface of the feedstock injector, inside the reactor. Once theceramic layer is ablated, the erosion of the steel is very rapid,leading to a substantial deterioration in the performance of theinjector.

Furthermore, the materials used for the manufacture of the injectorsalso limit the possible choice of the atomizing gas since the lattermust not induce significant corrosion of the material of the injector.This is the reason why steam is commonly used as atomizing gas. However,the oxygen atoms contained in the steam have a tendency to react withthe hydrocarbon feedstock or with the products of the cracking reaction,which may result in the formation of oxygen-containing compounds, whichare difficult to remove from the desired hydrocarbon product and are notvery reusable. Moreover, these oxygen-containing compounds may cause adeactivation of the catalysts used during subsequent treatmentoperations of the products obtained.

WO 2007/065001, U.S. Pat. Nos. 6,503,461, 5,061,457 and 4,875,996describe feedstock injectors, the end of which in contact with thecatalyst stream in the reaction zone comprises a ceramic element.However, the injectors described do not make it possible to avoid adegradation of their performance in service. This degradation does notappear to be linked to the ceramic head, for which no significantstructural modification is observed.

Consequently, a problem that is faced and that the present inventionaims to solve is not only that of providing an injector that isresistant to erosion and corrosion and that requires less maintenance,but also that of providing hydrocarbon feedstock injection means thatenable a better efficiency of the FCC unit and a better quality of theproducts obtained, while preserving their nebulization/atomizationperformance over time, and this being irrespective of the gas used fornebulizing/atomizing the feedstock.

For this purpose, the present invention proposes a feedstock injectorfor injecting a hydrocarbon feedstock into a tubular-type reactor withsubstantially upward or downward flow that is intended to be used in afluid catalytic cracking unit, having at least one hollow cylindricalbody, at least a first and a second inlet openings for respectivelyinjecting a liquid hydrocarbon feedstock to be cracked and an atomizinggas into said hollow cylindrical body, at least one contact chamberarranged inside said hollow cylindrical body, in which said liquidhydrocarbon feedstock to be cracked and said atomizing gas are intendedto be brought into contact in order to atomize said liquid hydrocarbonfeedstock to be cracked, and at least one outlet opening in order toeject said liquid hydrocarbon feedstock thus atomized, characterized inthat each element of the injector is formed of ceramic material.

Thus, one feature of the invention lies in the fact that the injector ismainly manufactured from a ceramic material. The injector according tothe invention has the advantage of being made of ceramic, at least asregards its main elements, namely the hollow cylindrical body, the inletopening for the atomizing gas, the inlet opening for the liquidhydrocarbon feedstock to be cracked and the contact chamber. Ceramicmaterials have proved suitable for the usage conditions of an FCC unit.In particular, these materials may have good corrosion resistance andthermal resistance. Ceramic materials have a relatively high hardness,greater than the catalysts used in the FCC unit, namely a hardness of atleast 1400 N/mm² as Vickers hardness. Preferably, the ceramic materialhas a hardness of greater than 2100 N/mm² or even greater than 2500N/mm². Owing to this relatively high hardness, the injectors accordingto the invention have the advantage of not requiring the presence of aprotective layer on their walls: it is thus no longer necessary toprotect the walls with coatings of the type of those described above forsteel walls. The result of this is a considerable weight saving of theinjectors with respect to the steel injectors customarily used, and asimplified manufacture.

Furthermore, owing to the high inertia of ceramics with respect to manychemical compounds, it is possible to broaden the choice of atomizinggases. In this case, it is possible to select atomizing gases that aremore reactive with the hydrocarbon products, or/and that cause onlylittle, or no, formation of oxygen-containing compounds. By way ofexample, mention may be made of gases that do not comprise any oxygenatoms, such as nitrogen, helium and hydrogen sulphide H₂S gases.

Without wishing to be tied to any one theory, the applicant assumes thatthe erosion/corrosion phenomena that take place inside conventionalinjectors, generally made of steel, in the zone for mixing of thefeedstock and the gas carrying out the nebulization/atomization of thefeedstock, would be at the root of the degradation of thenebulization/atomization performance over time, independently of thenature of the material used for manufacturing the injector head (steelor ceramic), the injector head being affected by other erosion phenomenapredominantly involving the cracking catalyst.

The feedstock injector according to the invention may be a two-phaseinjector. By way of example, mention may be made of “Venturi” or“impactor” injectors. However, the choice of the injector is not limitedas long as it produces droplets having, for example, a mean diameter ofthe same order as that of the catalyst particles (for example around70-80 microns).

Preferably, the ceramic material is selected from silicon carbide SiC,boron carbide B₄C, silicon nitride Si₃N₄, aluminium nitride AlN, boronnitride BN, alumina Al₂O₃, or mixtures thereof. Preferably, the ceramicmaterial is silicon carbide SiC.

Preferably, the ceramic material is silicon carbide SiC or comprisessilicon carbide SiC, preferably in a majority amount, for example in acontent of 60% to 99.9% by weight. Silicon carbide has the advantage ofpossessing good mechanical and physical properties for a reasonablemanufacturing cost.

As a variant, or optionally in combination, the ceramic materialcomprises a ceramic matrix selected from silicon carbide SiC, boroncarbide B₄C, silicon nitride Si₃N₄, aluminium nitride AlN, boron nitrideBN, alumina Al₂O₃, or mixtures thereof, incorporated in which ceramicmatrix are carbon fibres or ceramic fibres, or a mixture of thesefibres.

The ceramic material is then a composite material. Such a compositematerial may be advantageous for the injectors subjected to stretchingand shear stresses. In particular, the fibres may be positioned randomly(pseudo-isotropically) or anisotropically. An anisotropic distributionof the fibres may be advantageous in particular zones, for example theend zones intended to be assembled with another material or with anotherpart of the same material (mechanical assembly or welding, brazing) orin the case of zones subjected to a considerable stretching/shearstress. When they are present, these fibres may represent from 0.1% to10% by weight of the composite material.

The carbon fibres may be carbon fibres with graphite planes orientedalong the fibre.

The ceramic fibres may be selected from crystalline alumina fibres,mullite (3Al₂O₃, 2SiO₂) fibres, crystalline or amorphous silicon carbidefibres, zirconia fibres, silica-alumina fibres, or mixtures thereof.

Preferably, the composite ceramic material comprises a silicon carbideSiC matrix comprising fibres of the aforementioned type. Preferably, thefibres are silicon carbide fibres.

Advantageously and non-limitingly, the devices according to theinvention are preferably made of CMC materials (CMC=Ceramic MatrixComposite), here identified as CMC devices. In other words, thecomposite material here above mentioned may be a CMC.

A method of preparation of these CMC devices is preferably performed asfollows:

-   -   1) Shaping a fibrous ceramic material eventually over a        supporting material that could be removed without excessive        effort, in order to obtain a fibrous shape that can be        assimilated to the backbone of the final device to be obtained,        eventually in the presence of a first resin,    -   2) Coating the shape obtained at step (1) with finely divided        ceramic powder and at least a second resin, eventually in the        presence of finely divided carbon powder, to obtain a coated        shape,    -   3) Eventually repeat steps (1) and (2),    -   4) Heating the coated shape of step (2) or (3) under vacuum        and/or under inert atmosphere in order to transform the resins        of step (1), (2) and eventually (3) into a carbon-rich        structure, essentially deprived of other elements to obtain a        carbon-rich coated shape,    -   5) Introducing a gas within the carbon-rich coated shape of        step (4) under conditions efficient to transform the carbon-rich        structure into carbide containing carbon-rich structure,    -   6) Eventually removing the supporting material of step (1), when        present,

wherein carbon fibers are present at least at step (1), (2) and/or (3)within the fibrous ceramic material, within the finely divided ceramicpowder, within the finely divided carbon powder, and/or within the firstand/or second resin.

Preferably, the mixture of finely divided ceramic powder comprisesceramic fibers with lengths comprised between 100 nm to 5 mm in anamount from 0.1 to 20 Wt % relative to the total amount of finelydivided ceramic powder+finely divided carbon powder when present.

Preferably, the fibrous ceramic material is made of non-woven fabric,woven fabric or knit made with at least one of thread, yarn, string,filament, cord, string, bundle cable, eventually sewed to maintain thedesired shape. The fibrous ceramic material and the resins can bepresent in an amount up to 50 wt % relative to the total amount ofcomponents. In these conditions, if a CMC is manufactured with 50 Wt %fibrous ceramic material and resins, and ceramic powder comprising 20 Wt% ceramic fibers is added, the overall content in free fibers, i.e. notcontained in the fibrous ceramic material, before any thermal treatment,is 10 Wt %. (Wt %=weight percent).

The fibrous ceramic material is preferably made with carbon and/orsilicon carbide fibers.

The first, second and further resin are independently selected amongresins able to produce a carbon residue and to bind the differentconstituents of the ceramic material before thermal treatment. Suitableresins include preferably poly-methacrylic acid, poly methylmethacrylate, poly ethyl methacrylate, polymethacrylonitrile,polycarbonates, polyesters, polyolefins such as polyethylene andpolypropylene, polyurethanes, polyamides, polyvinyl butyral,polyoxyethylene, phenolic resins, furfuryl alcohol resins, usual polymerprecursors of carbon fibers such as polyacrylonitrile, rayon, petroleumpitch. The resins and their quantities are adjusted to the desiredporosity that is obtained after thermal treatment of step (4) and beforestep (5). Preferably, the total porosity after treatment of step (4)should be comprised between 15 vol % and 25 vol %, more preferablybetween 20 vol % and 22 vol %. (Vol %=volume percent). Without wishingto be bound by theory, it is assumed the resins, when undergoing thermaltreatment of step (4) transform into a network of cavities containingresidual carbon atoms surrounded with voids. It is assumed the gas ofstep (5) moves preferentially within this network thus allowing improvedhomogeneity in the final CMC material. For example, 78 Wt % SiC powderwhich contains 0.2 Wt % of silicon carbide fiber is mixed with 17 Wt %phenolic resin and 5 Wt % poly methyl methacrylate and this mixture isused to impregnate and cover a silicon carbide fabric (which accountsfor 20 Wt % of the overall weight) that surrounds a shaping support,then heated under inert gas atmosphere until complete carbonization ofthe resins to obtain a final product having from 16 vol % to 18 vol %total porosity.

The gas may be selected among SiH₄, SiCl₄, ZrCl₄, TiCl₄, BCl₃, to formcorresponding carbide.

Preferred gas is SiH₄ or SiCl₄.

Preferred conditions of step (5) are standard RCVI conditions (ReactiveChemical Vapor Infiltration), more preferably using pulsed pressure.

Preferably steps (4) and (5) are each independently performed at atemperature comprised between 1100 and 1800° C. and at an absolutepressure comprised between 0.1 and 1 bar.

Preferably, the finely divided ceramic powder comprises, or eventuallyconsists of, particles selected from silicon carbide SiC, boron carbideB₄C, silicon nitride Si₃N₄, aluminium nitride AlN, boron nitride BN,alumina Al₂O₃, or mixtures thereof.

Preferably, the finely divided carbon powder is carbon black.

A suitable but non limiting particle size range for the finely dividedceramic powder, and eventually finely divided carbon powder, is about 10micrometers or less.

Such a method of preparation allows improved homogeneity in the CMCmaterial in that porosity gradient and clogging at the surface of thematerial is considerably reduced or totally alleviated, depending on theexperimental conditions (low temperatures ca. 1100-1300° C. and reducedpressure ca. 0.1-0.5 bar abs. are preferred).

Advantageously and non-limitingly, the ceramic material may be asintered ceramic material. This may in particular facilitate theproduction of the elements made of ceramic, whether they are made fromone or more portions or whether the injector is produced from a singlepart. With regard to the dimension of the injectors, it is possible toproduce the injector according to the invention made of solid ceramic asa single part without assembling or welding. In this case, the injectormay be formed for example by moulding or by extrusion, followed by afiring of the green injection element, under conventional operatingconditions suitable for the type of ceramic produced. The firing step isoptionally preceded by a drying step.

Advantageously, the inner and/or outer walls of the injector may besmooth, in other words they may have a low surface roughness. Suchsmooth walls make it possible to increase the velocities in operationinside the injector and at the outlet opening. Therefore, it is possiblenot only to reduce the size of the injectors but also to increasethroughputs of hydrocarbon feedstock and consequently a betterdispersion of the hydrocarbon feedstock which makes it possible toimprove the quality of the cracking products from the hydrocarbonfeedstock. Furthermore, the fact of reducing the size of the injectorsmakes it possible to increase the number of injectors in the fluidizedbed.

Such a smooth wall may be obtained when the ceramic material is asintered ceramic material.

Advantageously and non-limitingly, the feedstock injector may beobtained from a relatively fine sintering powder, for example having amean grain diameter of less than or equal to 500 nm, which may result inrelatively smooth surfaces.

Alternatively or in addition, the feedstock injector may be obtained byadding to the main material, for example SiC, an additive selected fromboron B, silicon Si and carbon C, or mixtures thereof, for example in aproportion varying from 0.3% to 2% by weight. In the case of a SiCmaterial obtained by powder sintering, such an addition of additive maymake it possible to reduce the porosity and consequently the roughness.

Advantageously and non-limitingly, the additive may comprise a mixtureof boron B, silicon Si and carbon C. Additional SiC may thus be formed,which blocks the pores and thus reduces the roughness.

Alternatively or in addition, a step of additional deposition of SiC bychemical vapour deposition (CVD) could for example be provided.

In one particular embodiment, the elements of the injector may each bemade from a single part made of ceramic material, obtained by sintering.The sintering step may be preceded by a conventional shaping step, forexample by compression, extrusion or injection.

Sintering is a process for manufacturing parts that consists in heatinga powder without melting it. Under the effect of heat, the grains fusetogether, which forms the cohesion of the part. Sintering is especiallyused for obtaining the densification of ceramic materials and has thefollowing advantages:

-   -   it makes it possible to control the density of the substance; as        a powder is used to start with and since this powder does not        melt, it is possible to control the size of the powder grains        (particle size) and the density of the material, depending on        the degree of initial compacting of the powders;    -   it makes it possible to obtain materials having a controlled        porosity, that are chemically inert (low chemical reactivity and        good corrosion resistance) and thermally inert;    -   it makes it possible to control the dimensions of the parts        produced: as there is no change of state, the variations in        volume and in dimensions are not very large with respect to        melting (absence of shrinkage phenomenon).

In another particular embodiment, the elements of the injector may beseparate elements made of ceramic material that are assembled together.

Furthermore, each separate element of the injector, or at least one ofthe separate elements of the injector, may also be formed of severalportions assembled together. Each portion may in particular be obtainedby sintering.

The separate elements of the injector, and/or the portions forming theseelements, may be connected by welding or brazing. The assembling may forexample be carried out by a diffusion welding process, for example asdescribed in document US 2009/0239007 A1.

As a variant or in combination, separate elements of the injector to beassembled and/or portions forming these elements to be assembled mayhave ends shaped in order to be assembled by interlocking or screwing.

Advantageously, the ends of the portions or elements assembled byinterlocking or screwing may have a conical shape, which may make itpossible to simply reduce the stresses between the parts and to improvethe leaktightness between the parts.

Advantageously, for better leaktightness, a seal may be positionedbetween the portions or elements assembled by interlocking or screwing.It may be, for example, a seal made of carbon or made of any othersuitable material, for example made of vermiculite or made of anothercompressible and thermally stable material. Optionally, a seal may bepositioned between portions or elements assembled by interlocking orscrewing having a conical shape.

The injector according to the invention has the advantage of being madeof ceramic material, at least as regards its main elements, namelycylindrical body, inlet openings, outlet opening and contact chamber. Itmay however be possible to provide the injector with an externalreinforcement, in order to adapt to the physical stresses that will beencountered when the injector is in service.

In addition, the invention also relates to an ascending flow ordescending flow tubular-type reactor intended to be used in a fluidcatalytic cracking unit equipped with at least one feedstock injector ashas been defined above.

Advantageously, the reactor is equipped with at least two feedstockinjectors as defined above, and at least one of these injectors isoriented so as to inject a liquid hydrocarbon feedstockcounter-currently inside the reactor with respect to a flow direction ofthe stream of catalyst grains. This flow direction is generally parallelto the longitudinal axis of the reactor. In particular, the position ofthe feedstock injector(s) may be as described in document EP 0 911 379or EP 0 209 442.

By way of example, said at least one injector may be positioned so as toallow the introduction of the feedstock along a direction that makes anangle of 0 to 90° with the longitudinal axis of the reactor. This anglemay in particular be from 5 to 85°, or even from 30 to 60°. Theinjectors may thus be positioned so as to carry out an injection of thefeedstock counter-currently, optionally in combination with co-currentinjections, which may make it possible to ensure a better result asregards conversion of hydrocarbon feedstock and quality of the desiredproducts.

Given that it is no longer necessary to take into account the problem oferosion, the injector according to the invention may be positionedfreely so as to optimize the efficiency of the FCC. Such a positioningof injectors, optionally in combination with co-current injectors, maymake it possible to ensure a better result as regards conversion ofhydrocarbon feedstock and quality of the desired products.

Advantageously, when the tubular reactor is made of metal, for examplemade of stainless steel, it may be connected to at least one injector byfastening means capable of absorbing a difference in expansion betweenthe metal of the reactor and the ceramic material of said at least oneinjector.

For example, such fastening means may be formed by a layer of materialsessentially comprising assembled ceramic fibres having a non-zeroelastic modulus, this layer being positioned between a portion made ofceramic material and a metal portion and providing the cohesion of theseportions.

Alternatively, the geometry and the dimensions of the fastening meansmay be adapted in order to compensate for the difference in thermalexpansion between the metal and the ceramic material.

Such fastening means may comprise portions that interlock or screwtogether, preferably conical portions. For example, the portions to beassembled advantageously have a rotational symmetry, and their ends havecomplementary conical shapes.

As a variant, the fastening means may comprise one (or more) pressingelement(s) capable of exerting an elastic force on a portion made ofceramic material to be assembled to a metal portion in order to pressthis portion made of ceramic material against the metal portion.

Thus, the fastening withstands the differential expansion between thematerial of the metal portion, for example a steel, preferably astainless steel, and the ceramic material. Indeed, the ceramic may havea coefficient of thermal expansion that is much lower than that of thesteel.

The pressing element may for example comprise a spring means, or othermeans. It might be possible, for example, to provide one or morefastening tabs that are firmly attached to (or form a single part with)a metal portion, for example that are welded. These tabs, on the onehand welded via one end to the metal portion, while the other end restson a surface of a portion made of ceramic material, make it possible toexert an elastic bearing force on the portion made of ceramic materialso as to keep this portion pressed against the metal portion. This otherend may have a relatively flat surface in order to limit the zones ofhigh mechanical stresses.

In particular, the fastening means may comprise at least one metal tabfirmly attached to a fastening face of the reactor and capable ofexerting an elastic bearing force on an edge of an injector in order tokeep this edge elastically bearing against the fastening face of thereactor. The fastening face and the edge may extend over the entireperiphery of the ends to be assembled. They may be flanges.

As a variant, the tubular reactor may also be made of ceramic material.It may then be connected to said injector by welding, brazing, screwingor interlocking, as described above.

In particular, the ceramic material may be the same as that describedwith reference to the injector according to the invention, theassembling by welding, brazing, screwing or interlocking may be asdescribed with reference to the assembling of an injector made ofseveral separate portions.

The reactor made of ceramic material may itself be made from one or moreassembled portions made of ceramic material.

The invention also relates to a catalytic cracking unit comprising atleast one aforementioned injector and/or at least one reactor as definedabove.

The invention also relates to a fluid catalytic cracking processcomprising an injection of hydrocarbon feedstock into an ascending flowor descending flow tubular-type reactor, characterized in that saidinjection of feedstock comprises a prior step of bringing a liquidhydrocarbon feedstock to be cracked into contact with an atomizing gasusing at least one injector according to the invention, and in that saidatomizing gas consists substantially of a compound that does notcomprise any oxygen atoms.

Thus, steam is replaced by an atomizing gas that does not comprise anyoxygen atoms. This makes it possible to reduce the formation of theoxygen-containing compounds, which are difficult to remove from thedesired product.

The atomizing gas may be selected from inert gases such as nitrogen,helium and hydrogen or gases that react with olefins such as hydrogensulphide H₂S. Preferably, the compound is hydrogen sulphide H₂S.

Preferably, the liquid hydrocarbon feedstock is injected into saidreactor counter-currently with respect to a flow direction of the streamof catalyst grains. As already explained above, the flow direction isgenerally parallel to the longitudinal axis of the reactor. By way ofexample, the introduction of the feedstock along a direction makes anangle of 0 to 90° with the longitudinal axis of the reactor. This anglemay in particular be from 5 to 85°, or even from 30 to 60°.

Such a counter-current injection, optionally in combination withco-current injections, may make it possible to ensure a better result asregards conversion of hydrocarbon feedstock and quality of the desiredproducts.

Other distinctive features and advantages of the invention will emergeon reading the description given below of one particular embodiment ofthe invention, given by way of indication and non-limitingly, withreference to the appended drawings, in which:

FIG. 1 illustrates a schematic representation of an FCC unit;

FIG. 2 illustrates a schematic cross-sectional representation of aninjector, the subject of the invention according to a first variant;

FIG. 3 illustrates a schematic cross-sectional representation of aninjector, the subject of the invention according to a second variant;

FIGS. 4a and 4b are axial cross-sectional views of the ends of twoassembled parts. The assembled parts are separated in FIG. 4b forgreater clarity; and

FIG. 5 shows an example of assembling an injector according to theinvention to a reactor, in particular a metal reactor, FIG. 5a showing adetail from this FIG. 5.

FIG. 1 represents a fluid catalytic cracking unit equipped with anessentially ascending flow reactor. This unit is of a type known per se.It comprises in particular a column-shaped reactor 1, referred to as afeedstock riser, or riser, supplied at its base via a duct 32 withregenerated catalyst grains in a determined amount. A riser gas, forexample steam, is introduced into the column 1 through the line 4, bymeans of a diffuser 5.

The feedstock to be cracked is introduced at the injection zone 6, whichcomprises injectors 2 and 3 that will be described in detail below. Thecolumn 1 opens, at its top, into a chamber 9, referred to as adisengager, which is for example concentric with it and in which theseparation of the cracking products and the stripping of the deactivatedcatalyst particles are carried out. The cracking products are separatedfrom the spent catalyst particles in a cyclone 10, which is housed inthe chamber 9, at the top of which a line 11 is provided for dischargingthe cracking products, whilst the deactivated catalyst particles move bygravity towards the base of the chamber 9. A line 12 supplies fluidizinggas injectors or diffusers 13, uniformly arranged at the base of thechamber 9, with stripping fluid, generally steam. One or more othercyclones may be provided inside the chamber 9.

The deactivated catalyst particles thus stripped are discharged at thebase of the chamber 9 to a regenerator 14, through a duct 15, on which acontrol valve 16 is provided. In the regenerator 14, the coke depositedon the catalyst particles is burnt using air, injected at the base ofthe regenerator via a line 17, which supplies uniformly spaced injectorsor diffusers 18. The treated catalyst particles, entrained by the fluegas, are separated by cyclones 19, from where the flue gas is dischargedthrough a line 20, whilst the catalyst particles are discharged to thebase of the regenerator 14, from where they are recycled to the feed ofthe riser 1 via the duct 32, equipped with a control valve 33.

The reaction effluents are transported via the line 11 to afractionating column 25, which makes it possible to separate them bydistillation, in order to obtain:

-   -   through the line 26, the gaseous products (C1 to C4        hydrocarbons);    -   through the line 27, a petrol cut;    -   through the line 28, a diesel or LCO cut;    -   and finally, through the line 29, a distillation residue or        slurry cut, which contains significant amounts of fine        particles.

The ceramic injectors 2, 3 according to the invention may be installed,for example, in the lower portion of the riser 1.

FIG. 2 schematically represents an injector according to a firstembodiment of the invention. The injector 2′ is an injector commonlyreferred to as a “Venturi” type injector, having a hollow cylindricalbody 41. The injector 2′ has a first opening 40 and a second opening 42,each opening into a contact chamber 46 arranged inside the cylindricalbody 41. The injector 2′ additionally has an outlet opening 44 thatopens into the reactor 1 (not presented in FIG. 2).

The contact chamber 46 has a first introduction chamber 47 and a secondoutlet chamber 49, which communicate with one another via a neck 48having a diameter substantially smaller than that of the first andsecond chambers 47, 49.

The first opening 40 and the second opening 42 are respectively providedfor injecting the liquid hydrocarbon feedstock to be cracked, and forinjecting an atomizing gas into the injector. In this case, theatomizing gas may be steam but may be replaced by another gas, forexample hydrogen sulphide H₂S, hydrogen H₂ or refinery gas.

A refinery gas generally contains C1 to C5 hydrocarbons, hydrogen, andsometimes H₂S.

When the liquid hydrocarbon feedstock C is introduced through the firstopening 40, the liquid is guided by a path 50 that opens into the firstchamber 47. At the same time, the atomizing gas G introduced through thesecond opening 42 reaches the first chamber 47 in order to be mixed withthe liquid hydrocarbon feedstock. Next, the mixture of the atomizing gasand of the hydrocarbon liquid reaches sonic velocities at the neck 48owing to the Venturi effect. The increase in the velocity and the shearcaused by the atomizing gas cause the jet of liquid hydrocarbonfeedstock to break up into fine droplets.

The injector 2′ may be sized in order to operate with a stream of liquidat the neck of the order of 5000 kg/m²s. The atomization of the liquidhydrocarbon feedstock essentially takes place at the neck 48.

FIG. 3 schematically represents an injector according to a secondembodiment of the invention. The injector 2″ is an injector commonlyreferred to as an “impactor” type injector, which also has a hollowcylindrical body 141, arranged in which is a contact chamber 146.Structurally, the impactor type injector 2″ differs from that of Venturitype by the fact that:

-   -   the contact chamber 146 has a substantially constant internal        diameter, that is to say that it does not have a neck; and    -   the injector 2″ has a target 143 that juts out from an inner        wall 145 of the contact chamber 146 opposite the opening 142 for        introducing the atomizing gas G and through the passage of the        liquid hydrocarbon feedstock C.

The liquid hydrocarbon feedstock C is projected against the target 143,as soon as it enters the contact chamber 146 through a first opening140. The jet of liquid breaks up and is carried in the form of dropletsby a stream of atomizing gas G introduced through a second opening 142at high speed. The atomization of the liquid hydrocarbon feedstock inthis type of injector 2″ is carried out in two parts. A first part takesplace at the target 143 via a breakup of the jet of liquid hydrocarbonfeedstock. The second atomization takes place at an outlet opening 144of reduced diameter, where the narrowing of the diameter accelerates thefluids. By way of example, the outlet opening 144 has a diameter of theorder of 18 to 23 mm.

According to the invention, the injectors 2′, 2″ are formed entirelyfrom a ceramic material, preferably from silicon carbide SiC. They arefor example formed by injection moulding or extrusion. Injectionmoulding or extrusion are conventionally carried out using ceramicpowders or precursors of ceramics with a binder. According to anothermanufacturing method, the ceramic injectors are formed by compressionand heating of a ceramic powder, it being possible for the compressionto be maintained during the heating step, the heating step being a stepof sintering the ceramic powder. This technique is particularly wellsuited to the manufacture of solid elements made of silicon carbideaccording to the invention. The ceramic powder used optionally comprisesceramic fibres in order to increase the mechanical strength of the partsproduced. The ceramic fibres, when they are present, generally representfrom 0.1% to 10% by weight of the part produced.

According to the invention, the injector 2 is made from one or moreparts made of ceramic material. For example, the hollow cylindrical body41, 141 and the second inlet opening 42, 142 may be separate parts, itbeing possible for the hollow cylindrical body 41, 141 and the firstinlet opening 40, 140 to be made from a single part.

The elements 41 and 42 may then be interlocked, as representedschematically in FIG. 4a by interlocking of conical end portions ofcomplementary shape, or assembled by screwing of their ends (FIG. 4b ),or else welded or brazed (not represented). Similarly, the hollowcylindrical body 41, 141 may consist of several separate portions thatare assembled, it being possible for this assembling to be carried outas described above, by assembling cylindrical or conical sections, orelse by assembling parts resembling bricks by interlocking and/orwelding/brazing.

The injector 2 may be connected directly to an outer wall 1 a of thetubular reactor 1 as represented schematically in FIG. 5. When thetubular reactor 1 is made of metal, its outer wall 1 a may have afastening face 1 b, firmly attached to which are at least two metal tabs1 c shaped in order to bear against an edge 2 c of the injector 2 inorder to keep this edge 2 c bearing against the fastening face 1 b ofthe reactor. This edge 2 c may be located at one end of the injector 2.The fastening face 1 b and the edge 2 c may extend over the entireperiphery of the ends to be assembled. They may be flanges.

As a variant that is not represented, the reactor may also be made ofceramic material and the fastening to the injector may then be carriedout as described above for the assembling of the elements of theinjector.

The invention has been described with reference to an FCC unit operatingwith a riser reactor, the injectors according to the invention mayhowever also be used in FCC units operating with a downer reactor.

The invention claimed is:
 1. A fluid catalytic cracking processcomprising: injecting a hydrocarbon feedstock into a riser or downertubular-type reactor, the riser or downer tubular-type reactor beingpart of fluid catalytic cracking unit, wherein the injecting of thehydrocarbon feedstock comprises bringing a liquid hydrocarbon feedstockto be cracked into contact with an atomizing gas in order to atomize theliquid hydrocarbon feedstock using at least one feedstock injectorcomprising: at least one hollow cylindrical body; at least a first and asecond inlet openings for respectively injecting a liquid hydrocarbonfeedstock to be cracked and an atomizing gas into the cylindrical body;at least one contact chamber arranged inside the hollow cylindricalbody, in which the liquid hydrocarbon feedstock to be cracked and theatomizing gas are intended to be brought into contact in order toatomize the liquid hydrocarbon feedstock to be cracked; and at least oneoutlet opening that opens on the inside of the reactor in order to ejectthe liquid hydrocarbon feedstock thus atomized, characterized in thateach element of the injector is formed of a ceramic material, and theceramic material comprises a ceramic matrix selected from siliconcarbide SiC, boron carbide B₄C, silicon nitride Si₃N₄, aluminium nitrideAlN, boron nitride BN, alumina Al₂O₃, or mixtures thereof, incorporatedin which ceramic matrix are carbon fibres or ceramic fibres; and in thatthe atomizing gas consists of a compound that does not comprise anyoxygen atoms.
 2. The fluid catalytic cracking process according to claim1, characterized in that the compound is hydrogen sulphide H₂S.
 3. Thefluid catalytic cracking process according to claim 1, characterized inthat the liquid hydrocarbon feedstock is injected into the reactorcounter-currently with respect to a flow direction of the stream ofcatalyst grains.
 4. The fluid catalytic cracking process according toclaim 1, wherein the feedstock injector comprises ceramic fibresselected from crystalline alumina fibres, mullite fibres, crystalline oramorphous silicon carbide fibres, zirconia fibres, silica-aluminafibres, or mixtures thereof.
 5. The fluid catalytic cracking processaccording to claim 1, wherein the feedstock injector comprises a ceramicmaterial which is a sintered ceramic material.
 6. The fluid catalyticcracking process according to claim 1, wherein the feedstock injectorcomprises a ceramic material which is a Ceramic Matrix Composite namedCMC.
 7. The fluid catalytic cracking process according to claim 1,wherein the feedstock injector is formed as one part.
 8. The fluidcatalytic cracking process according to claim 1, wherein the riser ordowner tubular-type reactor for use in a fluid catalytic cracking unitcomprises the at least one feedstock injector.
 9. The fluid catalyticcracking process according to claim 1, wherein the riser or downertubular-type reactor is equipped with at least two feedstock injectors,and in that at least one of the injectors is oriented so as to inject aliquid hydrocarbon feedstock counter currently inside the reactor withrespect to a flow direction of the stream of catalyst grains.
 10. Thefluid catalytic cracking process according to claim 1, wherein the riseror downer tubular-type reactor is made of metal, and in that theinjector is connected to the reactor by fastening means capable ofabsorbing a difference in expansion between the metal of the reactor andthe ceramic material of the injector.
 11. The fluid catalytic crackingprocess according to claim 1, wherein the riser or downer tubular-typereactor is made of ceramic material and in that the injector isconnected to the reactor by welding, brazing, screwing or interlocking.